Electron storage device



Jan-20, 1959 -M. KNGU. mL 2,870,360

ELECTRONSTORAGE DEVICE Filed Jan. 15, 1954 ORNEY United States 'Patent'z,s70,360 ELECTRON SToRAGE DEVICE Y Max Knoll, Princeton, N. J., andPaul Rudnick, Fort Wayne, Ind., assignors, by mesneyassignments,` tothe- United States of America. as yrepresented by the Secretary of theArmy Application January 15, 1954, SerialNo; 404,3322 6 Claims.v (Cl.313468) In general, a storage tube is an electron tube into whichlinformation can be introduced and then extracted at a later time. In acharge-controlled ystorage tube the information is retained byv staticelectric charges. Such charges are generally retained on a homogeneousinsulating surface, on an insulating coating over a conducting mesh, oron an array of discrete insulated areas for definite periods of time, asneeded. It is desirable that the resistance of the storing materialremain as high as possible even at higher temperatures.

The action of establishing a charge -pattern corresponding to an inputsignal is known as writing; The-retentive feature of this actionmay alsobe referred to as storing. Retention of the stored charge pattern for aperiod of time is accomplished by means of the insulating properties Ofthe surface of a target electrode. In a viewing storage tube provisionis made for the formation of a visible imagecorresponding to the patternof stored charges.

The generation of an electrical or visual output signal corresponding tothe stored charge pattern is known as reading. Erasing takes place bythe removal `of a pre-- viously stored charge pattern with the aid ofsome controllable process such as secondary emission orphotoconductivity, and may be accomplished by the writing beam.

In certain types of storage tubes the storage insulator is located closeto some major source of heatv such as a large-area thermionic cathode.At the high temperatures there found, most insulating materials tend tolose their effectiveness in storingelectric charges. In these casesincreased temperature produces an exponential de'- crease'of specificresistance vof the material and the stored charges leak off.

It is therefore an object of this invention toprovide y an improvedelectronic device for the storage and visual presentation ofinformation, in which the insulating ma-v terial serving to store theinformation may be operated at high temperature and still be capable ofretaining information for a useful length of time.

A further object of this invention is to provide for use in a storagetube an improved insulating material which can retain a stored chargefor a longer period than can other storage material under changingambient'temperatures.

. The objects of the invention may be realized throughy an embodimentwhich makes use of a polymeriz'ed surface film formed over a' storagetarget electrode.- The-polymerized surface film may be formeddirectlyvoverthe conducting base of a target electrode or over the usual layerof magnesium'uoride, silica or otherinsulator used as the storageelement in an electronic storage device;

Thisiilm is of a hydrocarbon nature, polymerizedgfand'- is formed byelectron bombardment of a target electrode in a suitable yrareiiedhydrocarbon atmosphere.

2,870,360 Patented Jan. 20, 1959 ICC elevational sectionalfview of avviewing storage tube, in

accordance with the invention. i

Referring to the drawing, a viewing type storage tube 10 is shown havingan evacuated, substantially cylindrical envelope 20, for example, aglass bulb. Positioned within the cylindrical envelope 20fis a largeVthermionic cathodem 21 held in place by anelectrically conducting,cathodeV support 22 and so disposed near one end of the envelope 20 asto be capable of `'emitting a wide viewingbeamof electrons toward theother endof the envelope. .Heate r, element 23 is positioned within thethermionic cathode21` sufficiently close to the thermionic cathode v21to heatV it efficiently. The storage Vtarget electrode 24,' is held, in

place adjacentv to the thermionic cathode by electrically conductingtarget supports 25 .and 26..

The storage target electrode 24 associated with this invention may beany of the ,usual types. lts surface may be homogeneous ornmeshed. Theholespacing of the mesh is determined by the amount of resolutionVdesired. It may be made of woven wires or formed by etching orelectroplating. The invention, however, will be more fully vand easilyunderstood from a detailed description of a single type of targetsurface and for this purpose an y electro-formed mesh approximately .001of an inch thick and with about 200 grid openings per linear inch hasbeenf chosen. Each cross-grid 30, in this embodiment of then targetstructure, is of suchsize as to form apertures 31 which are equalincombinedarea to approximately 50% of the total target surface.

The usual storage layer 32, which may be magnesium fluoride, silica orsome other suitable insulator, is there shown formed over eachcross-grid 30. For purposes of clarity, storage layer 32 thicknessl hasbeen considerably exaggerated. According tov this invention apolymerized hydrocarbon'iilm 33 is deposited on the target electrode 24over the usual storage layer 32.

The large viewing beam of electrons which is emitted by the thermioniccathode 21 during operation is focused magnetically by a field from afocusing coil 36 to impinge on the luminescent viewing screen 38, at theend of the cylindrical envelope 20 opposite to a thermionic cathode 21,through the grounded aluminum layer 39. The aluminum layer 39 liesdirectly over the luminescent yviewing screen 38 and over a largepartofthe inner cylindrical surface of the envelope 20.

The writing gun'is placed within` the neck.61 of the lmage storage tube10 and so disposed as to be in a position -to emit a beam of electrons.62 in the directit'nn-y of the storage target electrode 24. The electrongun 60 comprises a cathode electrode 63, a control kelectrode 64,

a first accelerating kelectrode 66, a focusing electrode- 68, and asecond acceleratingelectrode 69. 'I'he foregomg electrodes form theelectron beam 62 emanating from the cathode 63 of the gun 60 into. asharply defined and focused beam. Separate pairs of deflection plates 72and 74`are provided for electrostatically deecting the beamin thedesired manner.

:The viewing storage tube shown in the drawing containsbo-th anelectronic storage system and elements whlch Vmalte the storedinformation visible for-an appreciable time from outside the tube.During operation, the largethermionic cathode 21'emits electronssubstantially unlformly over itsl whole surface in a large beam which 1sfocused magnetically by the field from focusing coil 36- onto `theluminescent viewing screen 38. In the absence of any modulation by thestorage targety electrode 24, the bombarded area of the screen isofunifo'rm brightness;

During a writing cycle,.withthe thermionic cathode 21` switched toground potential through: the switch 76, as y the writing gun 60 scansthe insulating film 33, it forms a pattern of charge or potential on theexposed surface of film 33 by any of the various known methods ofmodulation for storage tubes in which an incoming signal is fed to thecontrol grid 64, as described in the book Storage Tubes and Their BasicPrinciples by Knoll and Kazan and published in 1952 by John Wiley andSons. Suitable operating voltages are shown in the drawing. The storagetarget electrode may be set at a potential of zero to 100 voltsdepending upon the geometry of the particular tube. Then, during thereading part of the cycle, with the large thermionic cathode at -5,000volts with respect to ground, in regions of film 33 left with arelatively high negative charge with respect to the thermionic cathode21, the apertures 31 in the target electrode 24 will be closed toelectrons from thermionic cathode 21 by the field from this highnegative charge and will produce no luminescence on screen 38. Inregions which are relatively highly positive, all available electronsfrom the thermionic cathode 21 will penetrate the apertures 31 in thetarget electrode 24 and will be focused on the luminescent viewingscreen 38, giving highlights to the picture or other pattern ofinformation. Regions at intermediate potentials will allow smallerelectron currents from the thermionic cathode 21 to penetrate the targetelectrode 24 and bombard the luminescent viewing screen 38, yieldinghalf-tones. Thus the incoming electrical signal is converted into avisible picture containing desired information, which will persist untilthe next writing cycle leaves a different pattern on the insulating film33. The new and important feature of this device is the polymerizedhydrocarbon film 33 which makes possible the storage of charge orpotential patterns on an insulator in relatively close proximity to thehot cathode, as required in a storage tube of this type. It also makespossible other advantages which will be described.

Glass side tubes 77 and 78 are employed only during the process offorming the polymerized layer 33 over the target electrode 24 and aresealed off close to the envelope 2f) before actual operation of theviewing storage tube 10. A few drops of oil 80, preferably of low vacuumpressure (Octoil, for example) such as is used n oil diffusion vacuumpumps7 are left deposited in the glass bottle 79 the opening to which iscontrolled by valve-stopper 81.

Polymerization lof a hydrocarbon film over a storage target electrodemay conveniently be accomplished at room temperature. The storage targetelectrode is so disposed within the evacuated envelope of a storage tubeas to facilitate bombardment by an electron gun. An oil diffusion pumpis continuously operated to maintain a pressure of 10r5 mm. of mercury.If an electron gun, similar to the writing gun 60 in the neck of theimage storage tube 10 is chosen, it is operated at the voltages shown inFigure l except for the control grid which is maintained at-SOOO volts.Under these conditions an unfocused electron beam of approximately 1milliampere will be swept across the surface of the storage targetelectrode. A polymerized hydrocarbon film 0.1 micron thick would beformed over a storage target electrode approximately 3 cm. in diameterin approximately 24 hours or less depending on the residual gas pressurewithin the tube. The use of an inexpensive electron spray gun which iscapable of emitting an unfocused beam of 1GO milliamperes reduces thetime of formation of the film to approximately minutes. In the region ofthe values here used the rate of growth of the film is substantiallylinear' with beam current intensity.

For practical purposes a storage layer of the thickness of 0.1 to 10.0microns has been found effective. In general, for storage tubes layersof a thickness of 0.1 to 100 microns are used.

If an oil diEusion pump is used for the purpose of evacuating the glassenvelope suicient oil vapor is present in the atmosphere of thepartially evacuated envelope for the formation of the polymerizedhydrocarbon film. Where a mercury diffusion pump is used it may becomenecessary to introduce some oil vapor through the side tube 78 connectedto the bottle 79 into which has been deposited a few drops of some oilof low vacuum pressure.

The polymerized film may be formed either over the surface of some otherinsulating layer such as silica or magnesium uoride; or it may equallyeffectively beformed directly on the bare conducting base of the storagetarget electrode.

Similarly, the polymerized hydrocarbon lm may beformed over the storagetarget electrode Within a bell jar. If done in this manner the sameconditions prevail as would prevail under those circumstances where thefilm is formed in the envelope of the storage tube. An electron gun isprequired and is so disposed and activated that it can bombard a storagetarget electrode with a beam of adequate current intensity. Care must betaken however in removing the target electrode from the bell jar toprevent contamination.

Thus, by electron bombardment within a suitable atmosphere containingsmall amounts of oil vapor, a hydrocarbon film will be polymerized uponthe surface of a storage target electrode making it a highly effectiveinsulator for storage purposes.

The hydrocarbon film may be used as a storage element in all kinds ofcharge controlled storage tubes and its use is not limited to thestorage tube 10 described in the drawing herein. The use of thehydrocarbon iilm as a storage element carries with it other definiteadvantages. Storage tubes with a higher degree of vacuum can thus beproduced. The higher temperature required for processing of such tubesdoes not disintegrate the hydrocarbon film. Other insulating storagematerials frequently are evaporated in such processes.v Also, images maybe stored for long periods of time under high temperature. Furthermore,with the storagey grid at 220 C. the retention time of a polymerizedfilm has been observed to be ten times longer than that of uncoatedsilica at the same temperature. Television projection storage tubes ofthe transmission control type could be made to yield brighter images asneither the higher voltages nor the higher temperatures there requiredwould lower the effectiveness of the polymerized hydrocarbon storageelement.

What is claimed is:

l. An electron storage device comprising an electron gun for producing abeam of electrons along a path, an electrically conductive targetelectrode mounted transversely of said path, a layer of insulatingmaterial on said target electrode, and a polymerized film formed on thesaid layer of insulating material.

2. An electron storage device comprising an electron gun for producing abeam of electrons along a path, an electrically conductive targetelectrode mounted transversely of said path, a layer of insulatingmaterial on said target, and a polymerized hydrocarbon film formed onthe said layer of insulating material.

3. An electron storage device comprising an electron gun for producing abeam of electrons along a path, an

r electrically conductive target electrode mounted transversely of saidpath, a layer of insulating material on said target and facing said gun,and a polymerized hydrocarbon film formed on the said layer ofinsulating material.

4. An electron storage device comprising an evacuated envelope, anelectron gun within said envelope for the production of a beam ofelectrons along said path, an electrically conductive target electrodemounted within said envelope transversely to the said path, aninsulating coating on the surface of said target electrode, and apolymerized lm formed on said insulating coating.

5. An electron storage tube comprising an evacuated envelope, anelectron gun within the said envelope for the production of a beam ofelectrons along a path, a meshed electrically conductive targetelectrode mounted within said envelope transversely to the said path,and a polymer ized hydrocarbon lm on said meshed target electrode.

6. A target electrode, for an electron storage device, comprising anelectrically conductive target base, a layer of insulating material onsaid electrically conductive target base and a polymerizedhydrocarbon'iilm on said layer of insulating material.

References Cited in the tile of this patent UNITED STATES PATENTS JonesOct. 31, Knoll et al Nov. 21, Schulze Oct. 15, Klemperer Dec. 31,Sukumlyn May 5, Ross Sept. 21, Aichele July 27, Rudner Dec. 27,

1. AN ELECTRON STORAGE DEVICE COMPRISING AN ELECTRON GUN FOR PRODUCING ABEAM OF ELECTRONS ALONG A PATH, AN ELECTRICALLY CONDUCTIVE TARGETELECTRODE MOUNTED TRANSVERSELY OF SAID PATH, A LAYER OF INSULATINGMATERIAL ON SAID TARGET ELECTRODE, AND A POLYMERIZED FILM FORMED ON THESAID LAYER OF INSULATING MATERIAL.